Battery storage prices are falling at faster rate, similar to the sliding solar prices. According to McKinsey, the storage prices have come down to $230 per kilowatt-hour in 2016 from $1,000 per kilowatt-hour in 2010. With drop in cost, battery storage is fast emerging as a disruptive force in the energy market. Battery storage is no longer serving only as a grid balancing technology, rather it has emerged as a viable technology to replace conventional power generation, to ensure reliability and grid integration.

As solar power is also achieving grid parity, companies and researchers are focusing their attention to build better batteries. Not only energy companies, automobile manufacturers such as Tesla and Mercedes are also developing batteries that can store solar power and run the vehicles for long distances.

Lead acid, lithium-ion (Li-ion), nickel cadmium (NiCd or NiCad), nickel iron (NiFe) and flow batteries are commonly used for storing solar energy. However, lead acid and lithium-ion batteries are most popular choices. Here are some of the major batteries for storing power.

Lead acid: Lead acid continues to be the most popular rechargeable battery technology. These batteries possess deep-cycle characteristics and have highest capacity and long life cycle. Unlike other batteries, lead acid batteries can be charged faster and are less expensive compared to lithium-ion batteries. An inverter or charge controller is required to handle the battery charging. Flooded lead acid (FLA) batteries need to be refilled regularly with electrolyte, and proper ventilation should be provided to prevent accumulation of hydrogen gas. In the absorbed glass mat (AGM) and gel models of valve-regulated lead-acid (VRLA) batteries, hydrogen and oxygen are converted into water in the battery itself, eliminating the need for maintenance.










Image: Younicos commissions upgraded 3 mw system on kodiak island. Photo courtesy of YOUNICOS AG.

Lithium-ion: Lithium-ion (Li-ion) batteries are fast catching up with lead acid batteries. Low maintenance, high energy density, low self-discharge rate and long cycle life are factors contributing to the growing popularity of lithium-ion batteries. Because lithium-ion batteries require a battery management system (BMS) instead of an inverter, these batteries are significantly costlier than lead acid batteries. Lithium-ion batteries are lighter, do not require refills or maintenance, and are easy to install.

Nickel cadmium: Nickel cadmium (NiCd or NiCad) batteries have long life and reliability and do not require complex management systems, but do not possess the energy density of other batteries. However, they are much cheaper than other types of batteries. As nickel cadmium batteries can tolerate extreme temperatures, they are ideal for off-grid applications in large projects.










Image: SDG&E unveils 30MW lithium ion battery energy storage facility. Photo courtesy of San Diego Gas & Electric (SDG&E).

Nickel iron (NiFe): Nickel iron (NiFe) batteries have lower cycle life, high self-discharge rate, and lower energy density compared to lithium-ion or lead acid batteries. These factors make them less popular as solar storage option.

Flow batteries: Vanadium redox flow battery (VRFB) is a popular technology in flow batteries. These batteries use vanadium that is sourced from flyash. Flow batteries possess integrated power electronics that manage the charging and discharging processes. Older systems required equipment such as pumps, control units, sensors, and containment vessels, making them bulkier and occupy more space. Newer models include all these components within the container itself, reducing the space they occupy. Flow batteries last much longer than most other models, and can be charged and discharged completely.

Major manufacturers of solar batteries are: Tesla, sonnenBatterie, LG, Orison, Mercedes, NorthStar, Crown Battery, Su-Kam, Luminous, Eveready, and Amaron.










Image: Illustration of Tesla Powerpack lithium-ion battery and Hornsdale wind farm in South Africa. Photo: courtesy of Tesla.

LG Chem, a sister concern of LG Electronics, offers a lithium ion solar home battery that can be installed outdoor, and includes E-Gear energy management controller. The E-Gear controller allows the user to enable backup power and monitor self-consumption, giving visibility and control into the use, generation and storage of energy in the house.

The Sonnen solar battery, designed in Germany, is a popular choice for solar installations, as it has an intelligent energy management controller and 10,000 cycle life. This battery has already become popular in Europe.

Powerwall, a lithium-ion battery from American company Tesla, is ideal for new solar installations. However, it does not have the intelligent energy management controls that are present in other systems. Powerwall has a slim design and can be installed outside the house, making it an attractive option for non-solar customers as well.

Similar to Tesla, German automobile manufacturer Mercedes is also bringing a home battery that is similar to the Powerwall battery. The battery is being made available in Germany initially.

The Orison battery is a plug-and-play home battery system, which does not require professional setup. It can be mounted indoor on a wall or hidden behind furniture.

Companies such as NorthStar of Sweden, Crown Battery of US, besides Su-Kam, Luminous, Eveready and Amaron of India also have a range of solar batteries to choose from.

Lithium-ion batteries have the highest energy density per weight, and are much lighter and more efficient than lead acid batteries, but costly. However, lead acid batteries, being inexpensive, flexible for use in other applications and possessing consistent quality and performance, continue to be the best choice for solar power systems, that is, until lithium-ion batteries become affordable.